Conductance

Present address:Universit Denis Diderot (Paris 7), Groupe de Physique des Solides UMR 75 88, 2 place Jussieu, 75251 Paris Cedex 05, France. † Correspondence should be addressed to: [email protected] 1 We concentrate on results obtained for Pt wires, but conductance histograms suggest similar behaviour for Pd. The equilibrium H 2 gas pressure at a temperature of 4.2 K is about 10 −6 mbar.

In recent years, there is a tremendous interest and effort to control novel materials such as graphene to have desirable electric and magnetic properties via chemical, mechanical, and electrical manipulations . A particularly appealing approach is a dynamical engineering of materials, which offers a fascinating possibility to switch on and off properties at will . Here we propose a mechanism to dynamically control quantum transport in a class of semi-metals, such as graphene and topological insulators, via the application of light. In contrast to a conventional effect of light where photons induce current carriers by exciting electrons, we consider off-resonant, circularly polarized light which induces an effective gap in semi-metals. We analyze the transport properties of the resulting photo-induced non-equilibrium systems and show that graphene and surfaces of topological insulators exhibit insulating behaviors. Remarkably, these systems also exhibit quantum Hall effects in the absence of a magnetic field with a near quantization of the Hall conductance, realizing so-called quantum Hall systems without Landau levels . Our work opens new avenues for the study of quantum Hall effects in semi-metals and dynamical control of topological transport properties. arXiv:1104.4636v1 [cond-mat.mes-hall]

Central vestibular neurons play an important role in the processing of body motion-related multisensory signals and their transformation into motor commands for gaze and posture control. Over recent years, medial vestibular nucleus (MVN) neurons and to a lesser extent other vestibular neurons have been extensively studied in vivo and in vitro, in a range of species. These studies have begun to reveal how their intrinsic electrophysiological properties may relate to their response patterns, discharge dynamics and computational capabilities. In vitro studies indicate that MVN neurons are of two major subtypes (A and B), which differ in their spike shape and after-hyperpolarizations. This reflects differences in particular K + conductances present in the two subtypes, which also affect their response dynamics with type A cells having relatively lowfrequency dynamics (resembling ''tonic'' MVN cells in vivo) and type B cells having relatively high-frequency dynamics (resembling ''kinetic'' cells in vivo). The presence of more than one functional subtype of vestibular neuron seems to be a ubiquitous feature since vestibular neurons in the chick and frog also subdivide into populations with different, analogous electrophysiological properties. The ratio of type A to type B neurons appears to be plastic, and may be determined by the signal processing requirements of the vestibular system, which are species-variant. The membrane properties and discharge pattern of type A and type B MVN neurons develop largely post-natally, through the expression of the underlying ion channel conductances. The membrane properties of MVN neurons show rapid and long-lasting plastic changes after deafferentation (unilateral labyrinthectomy), which may serve to maintain their level of activity and excitability after the loss of afferent inputs.

We studied ion beam deposited NiFe/CoFe/Cu/CoFe/NiMn spin valves (SVs) subjected to different thermal annealing to establish the exchange field (H E ) of the CoFe pinned layer. The magnetoresistive (MR) properties of the SVs were characterized by magnetotransport measurements. We found MR values of 7.5%, 12% and 14% at T ¼ 20 K for SVs annealed at 453, 533 and 553 K, and observed a linear decrease of MR with increasing temperature for all SVs due to the excitation of spin waves. Our results also show that the exchange field H E is approximately constant over the measured temperature range (20-300 K) for SVs annealed at 453 and 553 K (H E % 250 and 400 Oe, respectively), while the sample annealed at 533 K shows the usual decrease of H E with temperature. These behaviors will be discussed in terms of structural differences between the measured SVs. An anomalous increase of the magnetoresistance at free layer switching in the ascending H-branch will be related with the enhancement of the pinned layer coercive field with decreasing temperature. r

Gap junctions connect cells in the bodies of all multicellular organisms, forming either homologous or heterologous (i.e. established between identical or different cell types, respectively) cell-to-cell contacts by utilizing identical (homotypic) or different (heterotypic) connexin protein subunits. Gap junctions in the nervous system serve electrical signaling between neurons, thus they are also called electrical synapses. Such electrical synapses are particularly abundant in the vertebrate retina where they are specialized to form links between neurons as well as glial cells. In this article, we summarize recent findings on retinal cell-to-cell coupling in different vertebrates and identify general features in the light of the evergrowing body of data. In particular, we describe and discuss tracer coupling patterns, connexin proteins, junctional conductances and modulatory processes. This multispecies comparison serves to point out that most features are remarkably conserved across the vertebrate classes, including (i) the cell types connected via electrical synapses; (ii) the connexin makeup and the conductance of each cell-tocell contact; (iii) the probable function of each gap junction in retinal circuitry; (iv) the fact that gap junctions underlie both electrical and/or tracer coupling between glial cells. These pan-vertebrate features thus demonstrate that retinal gap junctions have changed little during the over 500 million years of vertebrate evolution. Therefore, the fundamental architecture of electrically coupled retinal circuits seems as old as the retina itself, indicating that gap junctions deeply incorporated in retinal wiring from the very beginning of the eye formation of vertebrates. In addition to hard wiring provided by fast synaptic transmitter-releasing neurons and soft wiring contributed by peptidergic, aminergic and purinergic systems, electrical coupling may serve as the 'skeleton' of lateral processing, enabling important functions such as signal averaging and synchronization.

Cystic fibrosis (CF) is the most common, lethal inherited disorder in the Caucasian population. We have recently reported two African-American patients with nonsense mutations in each CF gene and severe pancreatic disease, but mild pulmonary disease. In order to examine the effect of these nonsense mutations on CF gene expression, bronchial and nasal epithelial cells were obtained from one of these patients (no. 246), a compound heterozygote for nonsense mutations R553X and W1316X; a healthy normal individual; a patient (no. 528) homozygous for the common CF mutation (AF508); and a CF patient (no. 272) who carries the R553X mutation and a missense mutation, S549N. When mRNA from bronchial cells of the normal individual, the AF508 homozygote, and the S549N/ R553X compound heterozygote was reverse transcribed and amplified by polymerase chain reaction using primers derived from the CF gene, DNA fragments of the predicted size were observed. However, patient no. 246 with nonsense mutations in each CF gene has no detectable cystic fibrosis transmembrane conductance regulator (CFTR) messenger RNA, and therefore should have severely diminished, and possibly absent, CFTIR protein. Furthermore, < 2% of the C1FTR transcripts in nasal epithelial cells from patient no. 272 (S549N/R553X) were derived from the gene with the nonsense mutation. We conclude that severe reduction in CFTR mRNA causes CF, but can have different consequences in the lung and pancreas.

Surfactin is a lipopeptide produced by certain strains of Bacillus subtilis and has potent surface activity. Here, we present the first results showing that ion-conducting pores can be formed by surfactin in artificial lipid membranes. With a low aqueous concentration of surfactin (1 pM) and a restricted membrane area (5-10-s cm 2) we observed conductance jumps that indicate the formation of individual ionic channels in the presence of K +, Rb +, Cs +, Na + or Li + chlorides. Although for every salt concentration (C i), the distribution in amplitude of the conductance steps (A i) may be rather broad, there is always a step amplitude which is more frequent than the others. In addition, the channels corresponding to this most frequent step amplitude are the longest in duration. For C~-1 M, the cationic selectivity sequence deduced from these most frequent events is K + > Rh + > Na + > Cs + = Li + with respective values for A/M: 130, 110, 80 and 30 pS. In KCi solutions AMo increases as a function of C i for low Ci, and shows a plateau for C/> 0.5 M. When measured on larger area membranes (10 °2 cm 2) with | M solutions of the monovalent salts KCI, NaO, RbC! and CsC! or the divalent salt CaC! z, the macroscopic low voltage conductance (G o) increases with a slope of 2 on a log-log plot as a function of surfactin concentration. These results demonstrate that surfactin produces selective cationic channels in lipid bilayer membranes and suggest that at higher salt concentratiou, a dhner is involved in this functional channel-forming process.

BIOME-BGC is a general ecosystem model designed to simulate hydrologic and biogeochemical processes across multiple scales. The objectives of this investigation were to compare BIOME-BGC estimates of hydrologic processes with observed data for different boreal forest stands and investigate factors that control simulated water fluxes. Model Iesults explained 62 and 98% of the respective variances in observed daily evapotranspiration and soil water; simulations of the onset of spring thaw and .the dates of snowpack disappearance and accumulation also generally tracked observations. Differences between o6served and simulated evapotranspiration were attributed to model assumptions of constant, growing season, overstory leaf areas that did not account for phenological changes and understory effects on stand daily water fluxes. Vapor pressure deficit and solar radiation accounted for 58-74% of the variances in simulated daily evapotranspiration during the growing season, though low air temperature and photosynthetic light levels were found to be the inajor limiting factors regulating simulated canopy conductances to water vapor. Humidity and soil moisture were generally not low enough to induce physiological wat~r stress in black spruce stands, though low soil water potentials resulted in approXimate 34% reductions in simulated me~n daily canopy conductances for aspen and jack pine stands. The sensitivity of evapotranspiration simulations to leaf area (LAI) was less than expected because of opposing responses of transpiration and evaporation to LAI. The resuJts of this investigation identify several components within boreal forest stands that are sensitive to climate change. chemical processes across multiple scales . Our goals are to utilize BIOMI;:-BGC logic to (1) synthesize and establish linkages between measured data at various spatial and temporal scales and (2) quantify key processes regulating wat~r fluxes. More specifically, we compareBIOME-BGC simulations of hydrologic processes for different boreal forest stands with daily evapotranspiration and soil water and snow depth measurements and investigate climate and stand characteristics that control simulated water fluxes. KIMBALL ET AL.: BIOME-BGC HYDROLOGIC SIMULAnONS FOR BOREAS

This paper documents the geometric optimisation of a three-dimensional micro-channel heat sink. The objective is to minimise the peak temperature from the walls to the coolant fluid. The optimisation is performed numerically by using the finite volume method. The numerical simulation was carried out on a unit cell with volume ranging from 0.1 mm 3 to 0.9 mm 3 and pressure drop between 10 kPa and 75 kPa. The axial length of the micro-channel heat sink was fixed at 10 mm. The cross-sectional area of the micro-channel heat sink is free to morph with respect to the degree of freedoms provided by the aspect ratio and the solid volume fraction. The effect of the total solid volume fraction and the pressure drop on the aspect ratio, channel hydraulic diameter and peak temperature is investigated. The numerical results show that the degrees of freedom have a strong effect on the peak temperature and the maximum thermal conductance. The optimal geometric characteristics obtained numerically (the aspect ratio and the optimal channel shape (hydraulic diameter)) are reported and compared with those obtained from approximate relationships using scale analysis. The predicted trends are found to be in good agreement with the numerical results.

Gold nanoparticle (Au NP) mirrors, which exhibit both high reflectance and electrical conductance, were self-assembled at a [heptane þ 1,2-dichloroethane]/water liquid/liquid interface. The highest reflectance, as observed experimentally and confirmed by finite difference time domain calculations, occurred for Au NP films consisting of 60 nm diameter NPs and approximate monolayer surface coverage. Scanning electrochemical microscopy approach curves over the interfacial metallic NP films revealed a transition from an insulating to a conducting electrical material on reaching a surface coverage at least equivalent to the formation of a single monolayer. Reflectance and conductance transitions were interpreted as critical junctures corresponding to a surface coverage that exceeded the percolation threshold of the Au NP films at the [heptane þ 1,2-dichloroethane]/water interface. KEYWORDS: surface plasmon resonance . Au nanoparticle mirror . liquid/liquid interface . reflectance . conductance . scanning electrochemical microscopy ARTICLE FANG ET AL.

The thick ascending limb of Henle mediates transcellular reabsorption of NaCl while generating a lumen-positive voltage that drives passive paracellular reabsorption of divalent cations. Disturbance of paracellular reabsorption leads to Ca 2+ and Mg 2+ wasting in patients with the rare inherited disorder of familial hypercalciuric hypomagnesemia with nephrocalcinosis (FHHNC). Recent work has shown that the claudin family of tight junction proteins form paracellular pores and determine the ion selectivity of paracellular permeability. Importantly, FHHNC has been found to be caused by mutations in two of these genes, claudin-16 and-19, and mice with knockdown of claudin-16 reproduce many of the features of FHHNC. Here, we review the physiology of TAL ion transport, present the current view of the role and mechanism of claudins in determining paracellular permeability, and discuss the possible pathogenic mechanisms responsible for FHHNC.

The dynamic clamp protocol allows an experimenter to simulate the presence of membrane conductances in, and synaptic connections between, biological neurons. Existing protocols and commercial ADC/DAC boards provide ready control in and between 52 neurons. Control at \2 sites is desirable when studying neural circuits with serial or ring connectivity. Here, we describe how to extend dynamic clamp control to four neurons and their associated synaptic interactions, using a single IBM-compatible PC, an ADC/DAC interface with two analog outputs, and an additional demultiplexing circuit. A specific C + + program, DYNCLAMP4, implements these procedures in a Windows environment, allowing one to change parameters while the dynamic clamp is running. Computational efficiency is increased by varying the duration of the input-output cycle. The program simulates 58 Hodgkin-Huxley-type conductances and 5 18 (chemical and/or electrical) synapses in 54 neurons and runs at a minimum update rate of 5 kHz on a 450 MHz CPU. (Increased speed is possible in a two-neuron version that does not need auxiliary circuitry). Using identified neurons of the crustacean stomatogastric ganglion, we illustrate on-line parameter modification and the construction of three-member synaptic rings.

We measured single-molecule conductances for three different redox systems self-assembled onto gold by the STMBJ method and compared them with electrochemical heterogeneous rate constants determined by ultrafast voltammetry. It was observed that fast systems indeed give higher conductance. Monotonous dependency of conductance on potential reveals that large molecular fluctuations prevent the molecular redox levels to lie in between the Fermi levels of the electrodes in the nanogap configuration. Electronic coupling factors for both experimental approaches were therefore evaluated based on the superexchange mechanism theory. The results suggest that coupling is surprisingly on the same order of magnitude or even larger in conductance measurements whereas electron transfer occurs on larger distances than in transient electrochemistry.

We have used a two-temperature nonequilibrium molecular dynamics method for predicting interfacial thermal resistance across metal-nonmetal interfaces. This method is an extension of the conventional nonequilibrium molecular dynamics for the dielectric-dielectric interface, where a temperature bias is imposed and the heat current is derived. We have included the electron degree of freedom for the interfacial thermal transport problem by treating the electron-phonon coupling with the two-temperature model. The method is demonstrated on two model systems, that is, silicon-copper interface and carbon-nanotube-copper interface. Temperature nonequilibrium between electrons and phonons in the metal side is quantitatively predicted, and a temperature drop across the interface is observed. The results agree with experimental data better than those obtained from conventional nonequilibrium molecular dynamics simulations where only phonons are considered. Our approach is capable of taking into account both the electron and lattice degrees of freedom in a single molecular dynamics simulation and is a generally useful tool for modeling interfacial thermal transport across metal-nonmetal interfaces.

Nanopores with fixed charges show ionic selectivity because of the high surface potential and the small pore radius. In this limit, the size of the ions could no longer be ignored because they occupy a significant fraction of the pore and, in addition, they would reach unrealistic concentrations at the surface if treated as point charges. However, most models of selectivity assume point ions and ignore this fact. Although this approach shows the essential qualitative trends of the problem, it is not strictly valid for high surface potentials and low nanopore radii, which is just the case where a high ionic selectivity should be expected. We consider the effect of ion size on the electrical double layer within a charged cylindrical nanopore using an extended Poisson-Boltzmann equation, paying special attention to (non-equilibrium) transport properties such as the streaming potential, the counter-ion transport number, and the electrical conductance. The first two quantities are related to the nanopore selectivity while the third one characterizes the conductive properties. We discuss the nanopore characteristics in terms of the ratio between the electrolyte and fixed charge concentrations and the ratio between the ionic and nanopore radii showing the experimental range where the point ion model can still be useful. Even for relatively small inorganic ions at intermediate concentrations, ion size effects could be significant for a quantitative estimation of the nanopore selectivity in the case of high surface charge densities.

Long-term potentiation (LTP) of AMPA receptor-mediated synaptic transmission at hippocampal CA1 synapses has been extensively studied, but the mechanisms responsible for its expression remain unresolved. We tested a hypothesis that there are multiple, developmentally regulated expression mechanisms by directly comparing LTP in hippocampal slices obtained from rats of two ages. At postnatal day 12 (P12), LTP was fully accounted for by an increase in potency (mean amplitude of responses excluding failures). This was associated with either an increase in AMPA receptor single-channel conductance (␥) or no change in ␥, suggesting an increase in the number of AMPA receptors. At P6, LTP was explained by an additional two mechanisms. In the majority of neurons, LTP was associated with an increase in success rate and a decrease in paired-pulse facilitation. In the remaining neurons, LTP was attributable to an increase in potency. However, in contrast to P12 neurons, the potency increase was associated with a decrease in ␥, suggesting the insertion of receptors with lower ␥. We conclude that there are multiple expression mechanisms for LTP at CA1 synapses that are developmentally regulated. These findings suggest that a single class of synapse uses a number of different molecular mechanisms to produce long-term changes in synaptic strength.

Two subarctic forested slopes in central Wolf Creek basin, Yukon, were studied in 1996±1997 to determine the seasonal pattern of the hydrologic processes. A south-facing slope has a dense aspen forest on silty soils with seasonal frost only and a north-facing slope has open stands of black spruce and an organic layer on top of clay sediments with permafrost. Snowmelt is advanced by approximately one month on the south-facing slope due to greater radiation receipt. Meltwater in®ltrates its seasonally frozen soil with low ice content, recharging the soil moisture reservoir but yielding no lateral surface or subsurface¯ow. Summer evaporation depletes this recharged moisture and any additional rainfall input, at the expense of surface or subsurface¯ow. The northfacing slope with an ice rich substrate hinders deep percolation. Snow meltwater is impounded within the organic layer to produce surface runo in rills and gullies, and subsurface¯ow along pipes and within the matrix of the organic soil. During the summer, most subsurface¯ows are con®ned to the organic layer which has hydraulic conductivities orders of magnitudes larger than the underlying boulder-clay. Evaporation on the north-facing slope declines as both the frost table and the water table descend in the summer. A water balance of the two slopes demonstrates that vertical processes of in®ltration and evaporation dominate moisture exchanges on the south-facing slope, whereas the retardation of deep drainage by frost and by clayey soil on the permafrost slope promotes a strong lateral¯ow component, principally within the organic layer. These results have the important implication that permafrost slopes and organic horizons are the principal controls on stream¯ow generation in subarctic catchments.

The terrestrial biosphere model Carbon Assimilation in the Biosphere (CARAIB) was improved by introducing two vegetation storeys and implementing a new module which simulates the equilibrium distribution of the vegetation inferred from physiological processes and climatic constraints. In this fourth version of CARAIB, we differentiate ground-level grasses from tree canopies, which allows us to determine the light available to grasses as a direct function of the leaf area index (LAI) of the forest canopy. Both of these storeys are potentially composed of several plant functional types (PFT). The cover fraction of each PFT within each storey is estimated according to its respective net primary productivity (NPP). A biome is assigned to each grid cell on the basis of three physiological criteria: (1) the cover fraction, (2) the NPP, and (3) the LAI; and two climatic constraints: (1) the growing degree-days (GDD) and (2) the lowest temperature reached during the cold season (T min ), which are well-known indices of vegetation expansion boundaries. Total biospheric carbon stocks (vegetation + soil) are reconstructed by forcing the model with eight climatic scenarios of the Last Glacial Maximum (LGM, 21 ka BP), which were obtained from the Paleo-Modelling Intercomparison Project (PMIP) from four general circulation models (MRI2, UGAMP, LMD4, and GEN2) using prescribed and computed sea surface temperatures (SSTs). The model was also forced with a current climate together with a preindustrial atmospheric CO 2 level of 280 ppm as reference simulation. To validate the model, current biome distribution is reconstructed and compared, for the modern climate, with two distributions of potential vegetation and, for the LGM, with pollen data. The model simulations are in good agreement with broad-scale patterns of vegetation distribution. The results indicate an increase in the total biospheric carbon stock of 827.8 -1106.1 Gt C since the LGM. Sensitivity analyses were performed to discriminate the relative effects of the atmospheric CO 2 level (''fertilization effect''), the climate (present or LGM), and the sea level. Our results suggest that the CO 2 fertilization effect is mostly responsible for the total increase in vegetation and soil carbon stocks. The four GCMs diverged in their predicted responses of continental climate to calculated SSTs. Only one of them, i.e., MRI2, predicted a marked decline of the continental temperatures in response to lower calculated SSTs. For this GCM, the effect of reduced SSTs on continental biospheric carbon stocks was a decrease of 544.1 Gt for the soil carbon stock and of 283.7 0921-8181/02/$ -see front matter D 2002 Elsevier Science B.V. All rights reserved. PII: S 0 9 2 1 -8 1 8 1 ( 0 2 ) 0 0 0 6 6 -8 (D. Otto).

Deciphering charge transport through multichannel pathwaysinsingle-molecule junctions is of high importance to construct nanoscale electronic devices and deepen insight into biological redoxp rocesses.H erein, we report two tailor-made folded single-molecule wires featuring intramolecular p-p stacking interactions.T he scanning tunneling microscope (STM) based break-junction technique and theoretical calculations showt hat through-bond and through-space conjugations are integrated into one single-molecule wire,allowing for two simultaneous conducting channels in as ingle-molecule junction. These folded molecules with stable p-p stacking interaction offer conceptual advances in single-molecule multichannel conductance,a nd are perfect models for conductance studies in biological systems,organic thin films,and p-stacked columnar aggregates.

Calcium chloride and snail physiological salt solutions were exposed to static magnetic fields (2.3-350 mT), and the physical properties of the solutions as well as their biologic effects were studied. Our preliminary observations show that these fields alter physicotions. Experiments on CaCI, solutions demonstrated field-dependent changes of electrical conductivity, with the magnitude and the direction of conductivity change being a function of both concentration and field intensity, The changcs in conductivity were maintained for periods in excess of I h after exposure. Conductivity changes were not found after exposure of physiological solutions to static magnetic fields. hut changes of biological consequence did occur. Other experiments showed [hat there were several changes in cellular function observed in ganglia and isolated neurons [) f~~,~/ .~/~~~/~7~/ / ; f~ when the perfusing medium was changed from the normal physiologic solution to the same solution after exposure to magnetic fields. These changes include membrane dcpolarization and increased action potential discharge, reduced uptake of Ca into cells, altered content of cyclic nucleotideh in ganglia. and increased volume of isolated cell bodies. A change in hydration of calcium ions may be one of the con<equences of magnetic-field exposure. and in physiological solutions this change may have functional consequences. OIYY4 hilcy-Li\\, Inc. chemical properties of CaClz solutions and the functional effects of physiologic, 'I I solu

Whole cell patch recordings have been realized in the primary visual cortex of the anesthetized and paralyzed cat, in order to better characterize input resistance and time constant of visual cortical cells in Lho. Measurements of conductance changes evoked by visual stimulation were derived from voltage clamp recordings achieved in continuous mode at two or more different subtreshold holding potentials. They show that the magnitude of the conductance increase can reach up to 300% of the mean conductance at rest. The observation of similar changes for the preferred and antagonist responses, when flashing ON and OFF, a test stimulus in pure ON and OFF subfields supports the hypothesis of a role for shunting inhibition in the spatial organization of simple receptive fields.

The only way to get a global, instantaneous picture of the energetic particle input over the auroral oval is through spectral imaging. The major driver of auroral emissions in the high-latitude ionosphere is overall electron precipitation. However, for certain locations and times, such as the equatorial edge of the evening auroral oval, proton precipitation can be the major energy source and thus the primary contributor to auroral emissions. Using kinetic transport models to describe the transport of energetic particles in the atmosphere, we analyze UV spectra from the STP78-1 satellite mission during magnetically disturbed conditions (Kp = 6) in the evening sector of the auroral oval. We discuss the contribution of protons and electrons to the auroral emissions. The energy flux of the incident protons is inferred from the H Lyman a emissions, after removing the H geocoronal background induced by solar radiation. Both the mean energy and energy flux of electron precipitation are inferred from non-H emissions (N II 108.5 nm, N 2 135.4 nm, and O I 135.6 nm), after removing the contribution of proton precipitation. From the latitudinal distribution of the incident energy flux the location of the electron and proton aurorae is discussed. The estimation of the particle characteristics allows one to infer the Pedersen and Hall electrical conductances induced by particle precipitation. For the studied substorm period, energetic protons contribute significantly to the Pedersen conductance, $25-30% overall of the total particle-induced conductances and much more at the equatorward edge of the midnight aurora. Because protons and electrons do not interact in the same way with the atmosphere, our study shows that while analyzing auroral spectra and studying the state of the ionosphere, it is crucial to separate electron and proton components of the precipitation. The method described to disentangle the relative contribution of precipitating electrons and protons may be applicable to the UV data of the upcoming TIMED and DMSP missions.

Wells placed next to surface-water bodies to induce infiltration have come under scrutiny because of the presence of the potential pathogens in surface water. Removal of pathogens and other contaminants by bank filtration is assumed, but regulatory agencies question the effectiveness of this process. To investigate transport processes of biological constituents, advective groundwater traveltimes to production wells under the influence of surface water need to be established first to determine appropriate water-quality sampling schedules.

The effect of acylated homoserine lactones (AHLs) and autoinducer-2 (AI-2) signalling compounds present in the cell-free culture supernatants (CFS), of Pseudomonas aeruginosa, Yersinia enterocolitica-like GTE 112, Serratia proteamaculans 00612, Y. enterocolitica CITY650 and Y. enterocolitica CITY844, on the growth of two Salmonella Enteritidis and two S. Typhimurium strains was assessed though monitoring of changes in conductance of the medium. Detection times (T det), area and slope of conductance curves were recorded. Except for P. aeruginosa 108928, which was not found to produce AI-2, all other strains produced both AHLs and AI-2. Thereafter, aliquots (20% in the final volume) of these CFS were transferred into NZ Amine broth inoculated with ca. 10 3 CFU/ml of stationary phase cultures of each Salmonella strain. While the CFS of P. aeruginosa induced a shorter detection time, i.e. acceleration of the metabolic activity, the CFS of the other microorganisms increased the detection time of Salmonella strains compared to control samples (i.e. without CFS). Results indicate that the growth of Salmonella may be affected by the presence of Quorum sensing (QS) signalling compounds and/or other novel signals existing in CFS, produced by other bacterial species and confirm the complexity of bacterial communication. The luxCDABE-encoded luminescence response of the reporter strain V. harveyi BB170 was used as the basis for determining AI-2 activity in CFS of tester strains. The assay was performed as described by Lu et al. 2004, and Nychas et al. 2009 2.6. Monitoring the effect of the CFS on Salmonella strains metabolic activity Growth of Salmonella strains was indirectly monitored by conductance measurements using the Malthus 2000 instrument (Radiometer International, Copenhagen, Denmark). A typical Malthus conductivity cell contains platinum

We establish some relations between the kinetics of incoherent, hopping charge transport in bridged large scale chemical systems or in a single-component duplex DNA, and the electrical properties (electric current (j) and conductance (g)) of these systems connected by two electrodes. We considered two distinct voltage distributions across the equienergetic chain (with N bridge elements, and an intersite hopping rate k), which involve the voltage being biased only across the edge bridge elements (case (i)), and the voltage being equally distributed across the bridge (case (ii)). For sufficiently long chains in the low voltage (U) domain, we find that j = (ek/N)G(j 1 ,j À1 )(eU/k B T), where G() is a function of charge injection rates j 1 (j À1 ) to (from) the electrode. The low field (constant) conductance is g = 1.6 · 10 À19 (k/N)G X À1 . At high voltages we established the existence of a maximal, constant, U independent current (j max ), where g ! 0. For case (i) j max = ek/N, being determined by the intersite hopping rate and by N À1 , as appropriate for diffusional charge transport. For case (ii) j max = ej 1 , being independent of the chain length, and determined by the rate of charge injection from the electrode. Finally, we applied our kinetic model for the description of incoherent charge transport in and the electronic properties of a donor-acceptor pair connected by two electrodes.

The control of agricultural pests is an important ecosystem service provided by predacious insects. In Midwestern USA, areas of remnant tallgrass prairie and prairie restorations may serve as relatively undisturbed sources of natural predators, and smaller areas of non-crop habitats such as seminatural areas and conservation plantings (CP) may serve as stepping stones across landscapes dominated by intensive agriculture. However, little is known about the flow of beneficial insects across large habitat networks. We measured abundance of soybean aphids and predators in 15 CP and adjacent soybean fields. We tested two hypotheses: (1) landscape connectivity enhances the flow of beneficial insects; and (2) prairies act as a source of sustaining populations of beneficial insects in well-connected habitats, by using adaptations of graph and circuit theory, respectively. For graph connectivity, incoming fluxes to the 15 CP from connected habitats were measured using an area-and distance-weighted flux metric with a range of negative exponential dispersal kernels. Distance was weighted by the percentage of seminatural area within ellipse-shaped landscapes, the shape of which was determined with correlated random walks. For circuit connectivity, effective conductance from the prairie to the individual 15 CP was measured by regarding the flux as conductance in a circuit. We used these two connectivity measures to predict the abundance of natural enemies in the selected sites. The most abundant predators were Anthocoridae, followed by exotic Coccinellidae, and native Coccinellidae. Predator abundances were explained well by aphid abundance. However, only native Coccinellidae were influenced by the flux and conductance. Interestingly, exotic Coccinellidae were negatively related to the flux, and native Coccinellidae were highly influenced by the interaction between exotic Coccinellidae and aphids. Our area-and distance-weighted flux and the conductance variables showed better fit to field data than area-weighted flux or Euclidean distance from the prairie. These results indicate that the network of seminatural areas has greater influence on the flow of native predators than that of exotic predators, and that the prairie acts as a source for native Coccinellidae. Managers can enhance conservation biocontrol and sustain the diversity of natural enemies by optimizing habitat networks.

An increase in cytosolic free calcium concentration [Ca 2 þ ] i initiates the exocytotic activity in various types of secretory cells. The guanosine 5′-O-[3-thio]triphosphate (GTPγS), a non-hydrolysable analogue of GTP (guanosine 5′-triphosphate), is an effective secretagogue for different cell types of different species, like mast cells, neutrophils or eosinophils. Consequently, the internal administration of GTPγS causes degranulation of mouse and rat mast cells. Regarding rat mast cells, it is proved that Ca 2 þ can cooperate with GTP or GTPγS in accelerating and increasing amplitude of the secretory response. All the previous studies with respect to capacitance recordings and mast cells were performed using mouse or rat mast cells, usually derived from peritoneum or the rat basophilic leukaemia cell line RBL. In this study, we applied the capacitance measurement technique to the human mast cell line-1 (HMC-1) cells, an immature cell line established from a patient with mast cell leukaemia. Patch-clamp dialysis experiments revealed that high intracellular free Ca 2 þ and GTPγS concentrations are both required for considerable capacitance increases in HMC-1 cells. During degranulation of HMC-1 cells, the total membrane capacitance (C m ) increase appeared continuously and, in some cases, as a discrete capacitance change, developing in a stepwise manner. Then, we tested the effect of latrunculin B upon HMC-1 cell capacitance increase as well as of some classic mast cell stimulators like PMA, A23187 and IL-1β in hexosaminidase release. Finally, we could conclude that the HMC-1 cell line represents a suitable model for the study of human mast cell degranulation.

The dynamic deformation upon stretching of Ni nanowires as those formed with mechanically controllable break junctions or with a scanning tunneling microscope is studied both experimentally and theoretically. Molecular dynamics simulations of the breaking process are performed. In addition, and in order to compare with experiments, we also compute the transport properties in the last stages before failure using the first-principles implementation of Landauer's formalism included in our transport package ALACANT.

Low-Temperature Mobility Measurements on CMOS Devices Abstracf-The surface channel mobility of carriers in n-and p-MOS transistors tabricated in a CMOS process was accurately determined at l o w temperatures down to 5 K. The mobility was obtained bJ an accurate measurement of the inversion charge density using a split C V technique and the conductance at low drain voltages. The split C-V technique was validated at all temperatures using a one-dimensional Poiswn ,oher (MOSCAP), which was modified for low-temperature application. The mobilitj dependence on the perpendicular electric field for different substrate bias balues appears to have different temperature dependence for n-and p-channel devices. The electron mobility increases with a decrease in temperature at all gate voltages. On the other hand, the hole mobilitj exhibits a different temperature behavior depending upon whether the gate voltage corresponds to strong inversion or i 5 near threshold.

Arundo donax L., commonly known as giant reed or Carrizo grande, has been identified as an excellent biomass feedstock, because of its high yields delivered from low nutrient inputs. Two criticisms of cultivating A. donax are that it has a history of biological invasion, and also that it may require great quantities of water to sustain its rapid growth. Yet, there is little research reported quantifying the water-use requirements; and it is unknown how growth and water-use will be altered by the atmospheric enrichment of carbon dioxide (CO 2 ) in combination with drought, two environmental conditions that have been predicted to occur in regions where A. donax is cultivated or has colonized. An experiment using close-topped CO 2 chambers was conducted to study the interactive effects of elevated CO 2 and limited water on A. donax growth and leaf physiology. Enrichment of atmospheric CO 2 from 400 to 800 mol mol −1 decreased transpiration rates by 100% (p < 0.05). Reduced transpiration delayed drought responses and extended periods of assimilation, but ultimately could not prevent desiccation and photosynthetic decline during extreme drought. Reduced transpiration also increased water use efficiencies (WUE). A linear model created from whole-plant water use estimates A. donax consumption at 186,500 and 139,500 L H 2 O Mg −1 (11.65 and 8.72 L H 2 O MJ −1 ), at 400 mol mol −1 or 800 mol mol −1 CO 2 respectively. The improved WUE of plants grown in high CO 2 was still less than values reported for Miscanthus, a C 4 bioenergy feedstock. Moreover, comparisons between A. donax stable carbon isotope ( 13 C) discrimination and values reported for other C 3 species suggest that A. donax has relatively high conductance levels, and will likely transpire more water than most species. These findings present the first reported values for A. donax water-use in response to atmospheric enrichment of CO 2 .

Variation in stomatal development and physiology of mature leaves from Alnus glutinosa plants grown under reference (current ambient, 360 µmol mol −" CO # ) and double ambient (720 µmol mol −" CO # ) carbon dioxide (CO # ) mole fractions is assessed in terms of relative plant growth, stomatal characters (i.e. stomatal index and density) and leaf photosynthetic characters. This is the first study to consider the effects of elevated CO # concentration on the distribution of stomata and epidermal cells across the whole leaf and to try to ascertain the cause of intraleaf variation. In general, a doubling of the atmospheric CO # concentration enhanced plant growth and significantly increased stomatal index. However, there was no significant change in relative stomatal density. Under elevated CO # concentration there was a significant decrease in stomatal conductance and an increase in assimilation rate. However, no significant differences were found for the maximum rate of carboxylation (V cmax ) and the light saturated rate of electron transport (J max ) between the control and elevated CO # treatment.

We present an experimental study of charge transport through single oligo(phenylene-ethynylene) (OPE3) molecules and anthracene substituted OPE3 (OPE3-AC) contacted with a mechanically controlled break junction. Both molecules are measured using two different methods. In the first approach, we measure the low-bias conductance, while the junction is repeatedly broken and fused. In the second approach, instead of applying a fixed bias, we record current-voltage characteristics. For both approaches the data is fitted to a model describing transport through a single level, and information about the level alignment and the electronic coupling to the electrodes is extracted. We find that the electronic coupling is similar for both molecules, but that the level alignment differs. The observed trends are confirmed by quantum chemistry calculations.

Brain computation, in the early visual system, is often considered as a hierarchical process in which features extracted in a given sensory relay are not present in previous stages of integration. In particular, orientation preference and its fine tuning selectivity are functional properties shared by most cortical cells and they are not observed at the preceding geniculate stage. A classical problem is identifying the mechanisms and circuitry underlying these computations. Several organizational principles have been proposed, giving different weights to the feedforward thalamocortical drive or to intracortical recurrent architectures. Within this context, an important issue is whether intracortical inhibition is fundamental for the genesis of stimulus selectivity, or rather normalizes spike response tuning with respect to other features such as stimulus strength or contrast, without influencing the selectivity bias and preference expressed in the excitatory input alone. We review here experimental observations concerning the presence or absence of inhibitory input evoked by non-preferred orientation/directions. Intracellular current clamp and voltage clamp recordings are analyzed in the light of new methods allowing us (1) to increase the visibility of inhibitory input, and (2) to continuously measure the visually evoked dynamics of input conductances. We conclude that there exists a diversity of synaptic input combinations generating the same profile of spike-based orientation selectivity, and that this diversity most likely reflects anatomical non-homogeneities in input sampling provided by the local context of the columnar and lateral intracortical network in which the considered cortical cell is embedded.

The purpose here is to reexamine the ecological importance of dew in arid and semiarid regions with a focus on the eastern Mediterranean area. This reevaluation is of particular importance under the controversial perspective that dew is insufficient as a source of water for plants but is sufficient to promote the spread of plant diseases. Adana, Turkey, was selected as an appropriate semiarid test ground with well-documented meteorological data and a newly developed photosynthesis and transpiration rate monitor (PTM), which was used to detect the response of transpiration and photosynthesis to the presence of dew on the leaves. A convolution theoretical model was used to simulate no-dew days; simultaneously, PTM measurements were used to obtain actual situations with dew. Contrary to expectations, we detected separate, early peaks of photosynthesis and late peaks of transpiration, leading to an average ratio of about 2:1 units of water use efficiency (WUE) for dew-affected versus no-dew conditions. The impressive performance of the dew-affected WUE was explained by a synergy between (1) low transpiration during dew-affected morning hours and (2) high CO 2 gradient toward the canopy. The first resulted from dew formation that created a humid environment in the near vicinity of the leaf followed by a low leaf to air vapor pressure deficit, which minimized transpiration. The second resulted from night respiration that induced a high CO 2 gradient from the air toward the canopy. This synergy resulted in intensive carbon intake at a low water cost and explained the ecological importance of dew.

Polymers are important as materials for manufacturing microfluidic devices for electrodriven separations, in which Joule heating is an unavoidable phenomenon. Heating effects were investigated in polymer capillaries using a CE setup. This study is the first step toward the longer-term objective of the study of heating effects occurring in polymeric microfluidic devices. The thermal conductivity of polymers is much smaller than that of fused silica (FS), resulting in less efficient dissipation of heat in polymeric capillaries. This study used conductance measurements as a temperature probe to determine the mean electrolyte temperatures in CE capillaries of different materials. Values for mean electrolyte temperatures in capillaries made of New Generation FluoroPolymer (NGFP), poly-(methylmethacrylate) (PMMA), and poly(ether ether ketone) (PEEK) capillaries were compared with those obtained for FS capillaries. Extrapolation of plots of conductance versus power per unit length (P/L) to zero power was used to obtain conductance values free of Joule heating effects. The ratio of the measured conductance values at different power levels to the conductance at zero power was used to determine the mean temperature of the electrolyte. For each type of capillary material, it was found that the average increase in the mean temperature of the electrolyte (DT Mean ) was directly proportional to P/L and inversely proportional to the thermal conductivity (l) of the capillary material. At 7.5 W/m, values for DT Mean for NGFP, PMMA, and PEEK were determined to be 36.6, 33.8, and 30.77C, respectively. Under identical conditions, DT Mean for FS capillaries was 20.47C.

The effect of glycerol on both micellar formation and the structural evolution of the sodium dodecyl sulfate (SDS) aggregates in the context of the action mechanism of the cosolvent has been studied. The critical micelle concentration and the degree of counterion dissociation of the surfactant over a temperature range from 208 8 8 8 8C to 408 8 8 8 8C were obtained by the conductance method. The thermodynamic parameters of micellization were estimated by using the equilibrium model of micelle formation. The analysis of these parameters indicated that the lower aggregation of the surfactant is mainly due to a minor cohesive energy of the mixed solvent system in relation to the pure water. The effect of glycerol on the mean aggregation number of the micelles of SDS was analyzed by the static quenching method. It was found that the aggregation number decreased with the glycerol content. This reduction in the micellar size seems to be controlled by an increase in the surface area per headgroup, which was ascribed to a participation of glycerol in the micellar solvation layer. Studies on the micropolarity of the aggregates, as sensed by the probe pyrene, indicated that this microenvironmental parameter is almost unaffected by the presence of glycerol in the mixture. However, an increase in the micellar microviscosity at the surface region was observed from the photophysical behavior of two different probes, rhodamine B and auramine O. These results suggest a certain interaction of the cosolvent in the micellar solvation of SDS micelles.

We show that in a layered metal, the angle dependent, finite frequency, interlayer magnetoresistance is altered due to the presence of a non-zero Berry curvature at the Fermi surface. At zero frequency, we find a conservation law which demands that the 'magic angle' condition for interlayer magnetoresistance extrema as a function of magnetic field tilt angle is essentially both field and Berry curvature independent. In the finite frequency case, however, we find that surprisingly large signatures of a finite Berry curvature occur in the periodic orbit resonances. We outline a method whereby the presence and magnitude of the Berry curvature at the Fermi surface can be extracted. * Electronic address: [email protected]

CO 2 fixation in a leaf is determined by biochemical and physical processes within the boundaries set by leaf structure. Traditionally determined temperature dependencies of biochemical processes include physical processes related to CO 2 exchange that result in inaccurate estimates of parameter values. • A realistic three-dimensional model of a birch ( Betula pendula ) leaf was used to distinguish between the physical and biochemical processes affecting the temperature dependence of CO 2 exchange, to determine new chloroplastic temperature dependencies for V c (max) and J max based on experiments, and to analyse mesophyll diffusion in detail. • The constraint created by dissolution of CO 2 at cell surfaces substantially decreased the CO 2 flux and its concentration inside chloroplasts, especially at high temperatures. Consequently, newly determined chloroplastic V c (max) and J max were more temperature dependent than originally. The role of carbonic anhydrase in mesophyll diffusion appeared to be minor under representative mid-day nonwater-limited conditions. • Leaf structure and physical processes significantly affect the apparent temperature dependence of CO 2 exchange, especially at optimal high temperatures when the photosynthetic sink is strong. The influence of three-dimensional leaf structure on the light environment inside a leaf is marked and affects the local choice between J max and V c (max) -limited assimilation rates. New Phytologist (2005) 166 : 205-215 www.newphytologist.org © New Phytologist (2005) Research 206 © New Phytologist (2005) www.newphytologist.org New Phytologist (2005) 166: 205-215 Research 207 New Phytologist (2005) 166: 205-215 www.newphytologist.org

Connexin37 (Cx37) forms gap junction channels between endothelial cells, and two polymorphic Cx37 variants (Cx37-S319 and Cx37-P319) have been identified with a possible link to atherosclerosis. We studied the gap junction channel properties of these hCx37 polymorphs by expression in stably transfected communication-deficient cells (N2A and RIN). We also expressed a third, truncated variant (Cx37-fs254⌬293) and Cx37 constructs containing epitope tags added to their amino or carboxyl termini. All Cx37 constructs were produced by the transfected cells as demonstrated by RT-PCR and immunoblotting and trafficked to appositional surfaces between cells as demonstrated by immunofluorescence microscopy. Dual whole cell patch-clamping studies demonstrated that Cx37-P319, Cx37-S319, and Cx37-fs254⌬293 had large unitary conductances (ϳ300 pS). However, addition of an amino terminal T7 tag (T7-Cx37-fs254⌬293) produced a single channel conductance of 120-145 pS with a 24-30 pS residual state. Moreover, the kinetics of the voltage-dependent decline in junctional current for T7-Cx37-fs254⌬293 were significantly slower than for the wild type, implying a destabilization of the transition state. These data suggest that the amino terminus of Cx37 plays a significant role in gating as well as conductance. The carboxyl terminal tail has lesser influence on unitary conductance and inactivation kinetics.